Knockout nanoparticles fight infection (RSC)

Septicaemia causing bacteria take a blow from two different types of antibacterial nanoparticles, made by scientists working independently in the UK and Korea.

 

With around 80% of the infections that patients pick up in hospital associated with bacteria on the surface of medical devices and biomaterials, effective antibacterial agents are highly sought after. Nanoparticle-based agents, often applied as coatings, have shown recent promise in delivering improved sterility against a wide range of bacterial strains.

Free silver nanoparticles show good antimicrobial activity, exhibiting both size- and shape-dependent microbiological activity. But, these free nanoparticles are unsuitable for some applications like wound dressings because of their sensitivity to light and temperature. They also form aggregates, which reduce dissolution rates and efficacy.

 

Adam Lee and co-workers at the University of York, UK, provide an alternative method of stabilising silver particles using a porous alumina solid to support nanoparticles of silver carbonate. Lee describes this material with its highly dispersed silver as 'alumina needles decorated with silver nanoparticles'. In this dispersed form the release rate of silver ions is maximised. And, the supported nanoparticles are 'easy to incorporate into the foam or fabric dressing formats that are essential to confine active silver species within patients' wounds over several days,' explains Lee.

In tests using the bacteria Staphylococcus aureus - responsible for a range of illnesses from minor skin infections to septicaemia - the team found that their nanoparticles were better antibacterial agents than silver sulfadiazine, which is a widely used topical treatment for severe burns and ulcers. 'And', says Lee, 'unlike many other silver preparations these nanoparticles are air- and light-stable, cheap to produce, nontoxic, nonallergenic and they don't stain clothing or skin during handling'.

Lee and his colleagues are now working with the medical products company Smith & Nephew to incorporate their nanoparticles into dressings suitable for patient trials in hospitals.

Korean scientists, Jyongsik Jang and Yura Kim at Seoul National University, are using an entirely different approach using antibacterial polymers, rather than silver, to create bioactive nanoparticles.

Using chemical polymerisation techniques Jang coated silica-core nanoparticles with a thin layer of antibacterial polymer. He found that these encapsulated nanoparticles have excellent efficacy against S. aureus and also Escherichia coli - the bacteria that causes food poisoning.

By varying the diameter of the silica core Jang obtained uniformly-sized particles that crucially do not aggregate, an undesirable trait because it reduces the active surface area. 'Antibacterial nanostructures with high surface areas provide enhanced efficacy compared to their bulk counterparts,' says Jang.

He describes some of the challenges for his future research: 'Key issues involve the separation and recovery of the antimicrobial nanoparticles from a target solution.' But, he says, 'the introduction of antimicrobial nanoparticles with magnetic properties could prove to be a clever solution'.